Interstitially coated compound and method of making the same



Patented Mar. 27, 1945 UNITED STATES PATENT OFFICE l v V 2,372,4o2

INTERSTITIALLY ooa'rnp coMroUNp AND METHOD or MAKING THE SAME William is. Stokes, Garden City, and William 1:. Barch, Farmingdale, N. Y., assigno'rs to Standard Brands Incorporated, New York, N. Y., a corporation of Delaware i no Drawing. Application January 22, 1941,

k a Serial No. 375,454

Claims. (01. 23-64) The invention relates to a methodfor treating crystalline compounds and to a product resulting therefrom. More particularly, it pertains'to a procedure for imparting a coating to crystalline compounds, and includes correlated improvements and discoveries whereby the properties of such compounds are modified.

An object of the invention is to provide a method in accordance with whichthe characteristics of a crystalline compound may be changed through treatment with a fatty compound.

An additional object of the invention is the provision of a method which serves to effect a combination of a fatty substance with a crystalline compound.

A further object of the invention is to provide a method whereby an absorption or interstitial coating of a crystalline compound by means of a fatty acid is brought about.

Another object of the invention is the provision of a method for accomplishing a combination between a'crystalline compound and a fatty substance in a ready, effective and economical manner.

A particular object of the invention is to provide a method for combining, as by interstitial coating, a fatty acid with a carbonate, especially a bicarbonate, so that the rate of reaction, e. g.

with an acid reacting substance, is controlled and retarded throughout the reaction period.

A specific object of the invention is the proviacid, whereby solubility and rateof reaction 5 are retarded throughout the course of the action. and being of unaltered appearance, free flowing and non-susceptible to 'removal of the fatty compound by mechanical abrasion.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the product possessing the featuresproperties, and the relation of constituents, which are exemplified in the followingdetailed disclosure, and the scope of the invention will be indicated in the claims.

In the practice of the invention a crystalline compound may be admixed with a fatty compound, preferably both in finely divided form, and the mix heated at an elevated temperature which lies above the melting point of the fatty compound but below the decomposition point of the crystalline compound until an interstitial combination-which may be both adsorption and absorptionhes been effected. A composition results having an unaltered original or uncombined appearance, and being free flowing and insensible to mechanical abrasion whereby the fatty compound would be at least in part removed. Such a combination or interstitial coating may be applied to various crystalline compounds, as carbonates, bicarbonates, tartrates, phosphates and the like, and more particularly the sodium, potassium and calcium compounds, as sodium bicarbonate, potassium bitartrate, calcium monophosphate and primary sodium phosphate.

-As fatty compounds utilization may be made of aliphatic monobasic saturated fatty acids. More particularly, the fatty acids which may be employed alone and in compatible admixtures may contain 12 to 24 carbon atoms, i. e., C12 to C24,,Sllch as lauric, myristic, palmitic, stearic and arachidic acids. The rate of interstitial combination or absorption is distinctly accelerated through the employment with the fatty compound of a small amount of a polyhydroxy compound, especiallypolyhydric alcohols, esters and acids as, for example, the glycols, erythritol, pentaerythritol, sorbitol, glucose, sorbitol stearate and the hexonic acids, as gluconic, mannonic and the like. The reaction or combination may be brought about by sieving together, as through an mesh sieve or screen, the crystalline compound and fatty compound with a polyhydric compound, and placing the admixture in a suitable vessel wherein it is heated at a temperature which is insuflicient to effect a decomposition of the crystalline compound but sufficient to cause melting of the fatty compound. While the mixture is being heated it may be stirred, preferably rapidly and continuously, until the fatty'compound is taken up or absorbed by the crystalline compound, which is usually indicated by the mix becoming dry and free from lumps. The composition may now be cooled, and is thereupon ready for use.

It is our observation that when the crystalline and fatty compounds, which may be sodium bicarbonate and stearlc acid, and these compounds will now be particularly specified for purpose of illustration, are intimately mixed in the dry state. or when stearic acid is dissolved in a solvent in which sodium bicarbonate is insoluble, no, appreciable reaction takes places, even when heated to C. for a considerable period. During heating the mass presents the characteristics of a mechanical mixture, 1. e. it is soft and sticky while hot, and lumpy and waxy when cold. Further, the rate of reaction of the sodium bicarbonate with acids is little affected by the stearic acid present on the surface. However, we observed that when the heating is conducted for a longer period a change begins to take place which is evidenced by a decrease in the sticky character while hot. As the heating is continued the composition finally becomes completely dry and loses entirely its waxy character, even at an elevated temperature.

Moreover, there is not any evolution of carbon dioxide, and no change in crystalline form of the sodium bicarbonate is discernible even under a microscope. Furthermore, there is no visible evidence of the presence of stearic acid which appears to have been completely taken up or absorbed into the lattice of the crystal without any reaction taking place. However, the stearic acid may be recovered, and quantitatively, by leaching out with a solvent, and an absorption or interstital combination amounting to about 8% by weight may be effected in this manner.

The rate of reaction of the sodium bicarbonate with acids has been profoundly modified through the combination, and this pertains not only to an initial retardation which would be occasioned by together, for example, four times through an 80 mesh screen. The admixture so produced may may be stirred rapidly and continuously until it is dry and free from lumps. This requires about minutes, and itis desirable that heating be continued for a further period of about 10 minutes so that the combination or absorption will be complete. When the mass has been heated for a sufficient time it may be cooled and is ready for a mere surface coating, but continuously so throughout the reaction period, or until all of the sodium bicarbonate has reacted. Additionally, the rate of combination or absorption under the same conditions for the same acid is substantially uniform, or, in other words, it takes as long to absorb the first gram as it does for the last gram. This rate decreases with increasing molecular weight of the fatty compound or acid, and it would appear that in the higher acids the molecule is too large to fit into the lattice structure of the crystal.

We have found that absorption of stearic acid by sodium bicarbonate when a polyhydric alcohol is present, as glycerol, requires only about five minutes at 100 C. The eifective amount of glycerol is rather small and may be of the order of about 1 part in 2000 parts of the crystalline compound. While polyhydroxy compounds of varied character, as above mentioned, may be utilized, nevertheless glycerol evidences the greatest eifect, i. e., it produces the most rapid absorption with the smallest amount. Glycerol is followed closely by sorbitol-which is somewhat more satisfactory for practical use inasmuch as it is a solid and is not hygroscopic.- It is believed that the result is due to an action which is other than strictly chemical. For example, sodium bicarbonate has a constant vapor pressure of water and carbon dioxide which increases with temperature. Because of this the crystal'surfaces and' interstices cannot be dried in the ordinary sense, and it seems probable that the progress of internal absorption or combination of the melted stearic acid is opposed by the continuous formation of water vapor. The polyhydroxy compounds are all soluble in melted stearic acid, are non-volatile, have a strong affinity for water and appear continuously to dry the pores or interstices through which the acid must pass.

As'an illustrative embodiment of a manner in which the invention may be practiced, the following example is presented. The parts are by weight.

About 100 parts of granular-sodium bicarbonate, 2.5 parts stearic acid-preferably U. S. P.,

' and 0.05 part crystalline sorbitol may be sieved utilization or packaging.

It has been found that a comminution or grinding of the product is not necessary but such may be done in the event that a more finely divided product is desired. Further, the sieving of the materials may be eliminated by first melting the stearic acid, dissolving the sorbitol in the molten acid and then adding the sodium bicarbonate with rapid stirring. The stearic acid should be distributed rapidly in order to avoid formation of lumps and an uneven coating. The amount of stearic acid above given has been found to be substantially the minimum amount necessary when the sodium bicarbonate is to be used in a baking preparation, since otherwise the volume of baked products, referred to as baking volumes, may not be wholly satisfactory due to a smaller amount giving smaller baking volumes. When larger amounts are employed there is an increasingly greater retardation of the rate of reaction, and consequently-the gas losses during mixing of a batter are smaller. However, this gain is offset by a slower action in the oven, and so much so that increasing the stearic acid from 2.5 parts to 4 parts while giving diiierent gas evolution curves shows approximately equal baking volumes.

It has been our finding that an amount larger than 4 parts yields smaller baking volumes due, itis believed, to a too slow an action in the oven, while when less than 2.5 parts are utilized smaller baking volumes also result, but in this case due to a greater loss during the initial or batter mixing period. If an equal weight of glycerol is substituted for the sorbitol the absorption time may be shortened from about 25 minutes to about 12 minutes. In the case of'other polyhydroxy compounds the absorption time is longer, for example, glucose requires about 45 minutes, and this rate is not susceptible to increase through the employment of larger amounts of the compound. That the polyhydroxy compound materially reduces the time is evidenced by the fact that without its presence a heating period of about three hours would be required, and the coating thus produced is not as satisfactory, either from the stand-point of evenness of distribution or of-baking value I Furthermore, a clear molten mixture may be obtained in the event that 0.5 part of the stearic acid is replaced by 0.5 part of a metal salt thereof, such as sodium, calcium, magnesium and aluminum stearates. The coatings so formed are higher melting and harder, but they do not give appreciably-different baking volumes unless the metal ion present is common to that which is present in the baking acid contained in the baking powder or composition, thus, calcium stearate and monocalcium phosphate. when such condiasraaoa 1 without departing from its scope, it is intended tion pertains, however, the bakingvolumes are markedly greater. Utilization of these combinations must be attended with care because of the likelihood that soda spots will form on the baked products.

Inasmuch as the coating is internal rather than superficial and retardation is exercised over the entire reaction period, a coated sodium bicarbonate may be utilized in the production of slow acting-baking powders even in coniunction with a fast acting acid substance. This leads to the results being better with more rapidly acting acid substances and relatively less so with those that are slow acting. Another factor plays a part in connection with the baking volumes obtained. Those acid substances which form an insoluble product of reaction, as tricalcium phosphate from calcium monophosphate, tend to clog the coating toward the end of the reaction period which suppresses gas evolution at that time. This is decided in the case of rapidly acting aluminum sulfate which forms aluminum hydroxide, and the reaction is totally suppressed at about 30% of completion. Consequently, more desirable results are obtained with rapidly acting primary sodium phosphate since an insoluble reaction product is not produced. That a marked increase in baking volume flows from the use of a coated sodium bicarbonate in a leavening composition is evidenced by the comparative volumes given in the following summary. These volumes are averages of a considerable number of bakings in which 500 grams of yellow cake batter were used under ordinary conditions of mixing and baking:

With coated soda With uncoated soda Primary sodium phosphate Tartaric acid Aluminum sulphate..." ......5

The foregoing procedure is attended by the following features. A crystalline compound is combined or coated with a fatty acid, whereby the rate of reaction is retarded throughout the reaction period. Thus, the rate of reaction of a bicarbonate with an acid substance is retarded, resulting in increased volume of products up to 20% when used as a leavening agent in baking. Further the coating material is absorbed or taken up internally into the crystal structure without decomposition ofthe crystalline compound, as loss of carbon dioxide in the case of a bicarbonate; the presence of a drying or dehydrating agent, whereby it is believed water formed constantly on the surface and in the interstices of the crystal is continuously removed as formed, results in a decided increase in the rate of absorption and an improved evenness of distribution of the coating substance; the coating matreated compounds, free-flowing and insensible to mechanical abrasion.

Since certain changes in carrying out the above process, and certain modifications in the composition which embody the invention may be made that all matter ,contained'jin the above description shall be interpreted as illustrative and not in a limiting sense. 1 v I It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention what we claim as new and desire to secure by Letters Patent is:

1. As a composition of matter a crystalline compound belonging to the group consisting of carbonates, bicarbonates, tartrates and phosphates having an interstitial coating containing a saturated fatty acid and a polyhydroxy compound produced by heating a mixture of said components until said mixture becomes dry, nonsticky, and free-flowing.

2. As a composition of matter a crystalline compound belonging to the group consisting of carbonates, bicarbonates, tartrates and phosphates having an interstitial coating containing a saturated fatty acid and a polyhydric alcohol produced by heating a mixture of said components until said mixture becomes dry, nonsticky, and free-flowing.

3. As a composition of matter sodium bicarbonate having an interstitial coating containing a saturated fatty acid and a polyhydroxy compound.

4. As a composition of matter sodium bicarbonate having an interstitial coating containing a saturated fatty acid and a polyhydric alcohol.

5, As a composition of matter sodium bicarbonate having an interstitial coating containing stearic acid and sorbitol.

6. A method for treating crystalline compounds which comprises admixing a crystalline compound belonging to the group consisting of carbonates, bicarbonates, tartrates and phosphates with a saturated fatty acid and a polyhydroxy compound and heating the admixture at a temperature between the melting point of the fatty acid and the decomposition point of the crystall ne compound until said fatty acid is interstitially taken up by said crystalline compound.

7. A method for treating crystalline compounds which comprises admixing a crystalline compound belonging to the group consisting of carbonates, bicarbonates, tartrates and phosphates with a saturated fatty acid and a polyhydric alcohol and heating the admixture at a temperature between the melting point of the fatty acid and the decomposition point of the crystalline compound until said fatty acid is interstitially taken up by said crystalline compound.

8. A method for treating crystalline compounds which comprises admixing a crystalline compound belonging to the group consisting of carbonates, bicarbonates, tartrates and phosphates with a saturated fatty acid and sorbitol and heating the admixture at a temperature between the melting point of the fatty acid and the decomposition point of the crystalline compound untl said fatty acid is interstitially taken up by said crystalline compound.

9. A method for treating crystalline sodium bicarbonate which comprises admixing sodium bicarbonate with a saturated fatty acid and a polyhydroxy compound and heating the admixture at a temperature between the melting point of the iatty acid and the decompofltion point of the sodium bicarbonate until said fatty acid is interstitially taken up by said bicarbonate.

10. A method for treating crystalline sodium bicarbonate which comprises admixing sodium 5 bicarbonate with a saturated fatty acid and aorbitol and heatin the admixture at a temperature between-the melting point or the fatty acid and the decomposition point of the sodium bicarbonate until said fatty acid is interstitlelly taken up by said bicarbonate.

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